1. Field of the Invention
The invention relates to a method of modifying the surface of polymeric substrate materials, such as woven polymeric textile surface formations, fibers or sheets, by means of electron bombardment, in a low pressure discharge medium, for the purpose of producing chemical and/or physical changes in these surfaces, thereby improving the technological properties thereof.
2. Description of the Prior Art
Methods and equipment for modifying the surfaces of polymeric solid bodies through bombardment with high-energy electrons are known. In this respect, electron accelerators which impart to the electrons energy amounting to 100 kiloelectron volts up to several megaelectron volts are used. Such equipment may include Van de Graaff generators or insulated core transformers. The essential feature of such a irradiation process is that the depth of penetration of the electrons into the solid body which is dependent upon the amount of the electron energy supplied is greater than the thickness of the substrate material.
Electron accelerators are very expensive and the necessary means for producing high voltage, and for guiding the beam often exceed the capacities of the equipment on hand. Moreover, major safety measures must be employed in order to protect the operating personnel from harmful radiation effects.
Still further, methods and equipment are known, wherein the surface of the solid body to be treated is brought in contact with ionized gases. The ionized gas is produced by glow, corona, or spark discharge. In such methods, interaction takes place between the free electrons, the ions and the excited neutral particles present in the discharge, and the solid body surface. However, the interaction energies amount only to a few electron volts, on the average. The energy of the electrons impinging on to solid body surfaces in these gas discharge installations, are less, by several orders of magnitude than those electron energies which are produced by the accelerator method, which causes their depth of penetration to be limited to less than 1 micrometer. Having regard to the technical expense and the operational protective measures, plasma plants give rise to less problems then electron accelerators, although, for the continuous operation of vacuum treatment plant, locks with pumps of high suction capacity are necessary. However, in the known gas discharge treatment installations, only the energy depleted and weak diffusion currents of the charge carriers are utilized, so that, due to the required exposure time of a few minutes necessary to obtain the desired technological effects, the productivity of these installations is inadequate for many technical uses.
Representative prior art, as above described, may be found in U.S. Pat. No. 3,179,482 to Kassenbeck, issued Apr. 20, 1965 and U.S. Pat. No. 3,600,122 to Coleman, issued Aug. 17, 1971. The former patent discloses a process of treating, particularly for dyeing wool, for example, by subjecting the substrate material to ionic bombardment for periods not less than 3 minutes and up to 10 minutes, and then subjecting the treated material to a dyeing medium. The latter patent disclosss a two zone system of grafting an ethylenically unsaturated monomer to a polymeric substrate. The first zone involves moving the substrate through a "spark discharge" in a first zone containing an initiator gas. Following activation of the surface, the substrate is moved to a second zone in which the activated surface is exposed to a free radical reactive substance that chemically reacts with the free radical sites.